Kohler Courage died

My buddy was mulching leaves and doing the last mow of the season with his Cub Cadet rider with Kohler Courage 20hp when it died. It acts like it is out of time. Try to crank, it hits a spot and stops. Not mechanical contact type stop, but compression. Put jumper cables on it and still the same. If I help it past TDC by turning it slowly by hand, it will crank over a couple times and seems to be backfiring. Couldnt tell if through intake or exhaust. Is there a common problem I should check first like the keyway or something? I plan on starting with a compression and leakdown test.. any direction much appreciated.

Do you have a serial number on this engine? I could be a non working compression release. If that is the case it might have also broken the exhaust valve keeper which could explain why it just quit running. It could be the flywheel key as darryl suggested. That would explain the engine quitting but not why it won't turn over. As for the gear on the crankshaft turning that can't happen on the Courage. It can on the Command but this Courage single has a keyed gear and plastic cam gears.

I meant to get the #'s off of it today but forgot. I took the good battery out of my SCag and it acted the same. While cranking, it turned over and stopped as the compression gauge jumped to 60, jumped to 90 on second try. Sounds like the compression release may not be working. I won't be able to look at it again until at least the weekend, but feel free to throw out any ideas or details.

90 psi shouldn't be a problem but in this business I've learned to never say never. Normally if the compression release isn't working you'd have over 120 psi compression. How does the engine turn over with the spark plug out?

The rocker arm on the exhaust fell off. I think the shop that serviced it earlier this year may not have gotten the lock nut tight enough. After I put that back on and adjusted, it started but was knocking. Several of the bolts that hold the side cover of the case were loose and it was leaking oil. After I tightened them the knock went away. Any thoughts on what may have caused that?

No telling, I had something similar happen with a brand new one (less than 8 hours), wasn't too happy with that but at least it's ran since without a hitch, I figure just be glad it was something you could fix.